Isometric 30° seems to behave like dimetric 26.6° (Blender 2.8)
I misunderstood the Wikipedia article. The angle 26.565° is the angle between projected non-vertical axes, and the horizontal line:



While the angle of the camera should indeed be 30° from the horizontal / 60° from the vertical:



To those, who want to achieve true Isometry in Blender, instead of the pseudo-isometry that I need, you actually have to set the angle of the camera to 35.264°.